1. Field of the Invention
The present invention relates to a power roller unit and an output disc unit for a toroidal type continuously variable transmission and more particularly, it relates to a power roller unit and an output disc unit which can make an assembling operation easy as for a toroidal type continuously variable transmission used, for example, as a transmission for a motor vehicle or a transmissions for various industrial machines, and can improve performance thereof by improving accuracy.
2. Related Background Art
As a transmission for a motor vehicle, use of a toroidal type continuously variable transmission as shown in FIGS. 21 and 22 has been investigated. For example, as disclosed in Japanese Utility Model Application Laid-open No. 62-71465 (1987), in the toroidal type continuously variable transmission, an input disc 2 is supported in coaxial with an input shaft 1 and an output disc 4 is secured to an end of an output shaft 3 disposed coaxially with the input shaft 1. Within a casing containing the toroidal type continuously variable transmission, there are provided trunnions 6 rockable around pivot shafts 5 disposed in twisted relations to the input shaft 1 and the output shaft 3.
That is to say, the pivot shafts 5 are provided on outer surfaces of these trunnions 6 at both ends thereof in a coaxial relation. Intermediate portions of the trunnions 6 support proximal ends of displacement shafts 7 so that, when the trunnions 6 are rocked around the pivot shafts 5, inclined angles of the displacement shafts 7 can be adjusted. Power rollers 8 are rotatably supported around the displacement shafts 7 supported by the trunnions 6. The power rollers 8 are interposed between opposed inner surfaces 2a, 4a of an input disc 2 and of an output disc 4. Each of the inner surfaces 2a, 4a has a concave surface obtained by rotating an arc around each pivot shaft 5. Peripheral surfaces 8a (formed as spherical convex surfaces) of the power rollers 8 abut against the inner surfaces 2a, 4a.
An urging device 9 of loading cam type is disposed between the input shaft 1 and the input disc 2 so that the input disc 2 can be urged elastically toward the output disc 4 by the urging device 9. The urging device 9 comprises a cam plate 10 rotated together with the input shaft 1, a plurality (for example, four) of rollers 12 rotatably retained (held) by a retainer (holder) 11. A drive cam surface (circumferential uneven (convex and concave) surface) 13 is formed one side (left side surface in FIGS. 21 and 22) of the cam plate 10, and a driven cam surface 14 having similar configuration is formed on an outer surface (right side surface in FIGS. 21 and 22) of the input disc 2. The plurality of rollers 12 are supported for rotation around shafts directed radially with respect to a center of the input shaft 1.
In use of the toroidal type continuously variable transmission having the above-mentioned construction, when the cam plate 10 is rotated as the input shaft 1 is rotated, the drive cam surface 13 urges the plurality of rollers 12 against the driven cam surface 14 formed on the outer surface of the input disc 2. As a result, the input disc 2 is urged against the power rollers 8, and, at the same time, the input disc 2 is rotated by the urging force between the drive and driven cam surfaces 13, 14 and the plurality of rollers 12. The rotation of the input disc 2 is transmitted to the output disc 4 through the power rollers 8, thereby rotating the output shaft 3 secured to the output disc 4.
When a rotational speed ratio (transmission ratio) between the input shaft 1 and the output shaft 3 is changed, and particularly when the speed reduction is effected between the input shaft 1 and the output shaft 3, the trunnions 6 are rotated in predetermined directions around the pivot shafts 5. And, the displacement shafts 7 are inclined so that the peripheral surfaces 8a of the power rollers 8 abut against a center side portion of the inner surface 2a of the input disc 2 and a peripheral side portion of the inner surface 4a of the output disc 4, respectively, as shown in FIG. 21. On the other hand, when speed increase is effected, the trunnions 6 are rotated in reverse directions around the pivot shafts 5. And, the displacement shafts 7 are inclined so that the peripheral surfaces 8a of the power rollers 8 abut against a peripheral side portion of the inner surface 2a of the input disc 2 and a center side portion of the inner surface 4a of the output disc 4, respectively, as shown in FIG. 22. When the inclination angles of the displacement shafts 7 are selected to intermediate values between FIG. 21 and FIG. 22, an intermediate transmission ratio can be obtained between the input shaft 1 and the output shaft 3.
FIGS. 23 and 24 show an example of a more concrete toroidal type continuously variable transmission disclosed in Japanese Utility Model Laid-open No. 1-173552 (1989). An input disc 2 and an output disc 4 are rotatably supported around a circular tubular input shaft 15 via needle bearings 16, respectively. A cam plate 10 is spline-connected to a peripheral surface of an end (left end in FIG. 23) of the input shaft 15 and is prevented from shifting a way from the input disc 2 by a flange 17. The cam plate 10 and a plurality of rollers 12 constitute an urging device 9 of loading cam type for rotating the input disc 2 while urging the input disc toward the output disc 4 on the basis of rotation of the input shaft 15. An output gear 18 is coupled to the output shaft 4 via keys 19 so that the input disc 4 and the output gear 18 can be rotated in a synchronous manner.
Both ends of a pair of trunnions 6 are supported by a pair of support plates 20 for rocking movement and displacement movement in an axial direction (direction perpendicular to the plane of FIG. 23; left-and-right direction in FIG. 24). That is to say, radial needle bearings (first radial bearings) 22 are provided between outer peripheral surfaces of pivot shafts 5 secured to the both ends of the trunnions 6 and inner peripheral surfaces of circular holes 21 formed in both ends of the support plates 20. Outer peripheral surfaces of outer races 23 of the radial needle bearings 22 are spherical convex surfaces so that these races are inserted within the circular holes 21 for rocking movement and axial displacement movement.
Displacement shafts 7 are supported within circular holes 24 formed in intermediate portions of the trunnions 6 supported between the pair of support plates 20 for rocking movement and axial displacement movement in this way. The displacement shaft 7 have support shaft portions 25 and pivot shaft portions 26 which are parallel with each other and eccentric (offset) from each other. The support shaft portions 25 are rotatably supported within the circular holes 24 via radial needle bearings (second radial bearings) 27. Power rollers 8 are rotatably supported around the pivot shaft portions 26 via radial needle bearings (third radial bearings) 28.
Incidentally, the pair of displacement shafts 7 are diametrically opposed with each other with respect to the input shaft 15. Directions of offset of the pivot shaft portions 26 of the displacement shafts 7 with respect to the support shaft portions 25 are the same (left and right opposite directions in FIG. 24) with respect to the rotational direction of the input and output discs 2, 4. Further, the offset directions are substantially perpendicular to the direction of the input shaft 15. Accordingly, the power rollers 8 are supported for a slight displacement movement in the direction of the input shaft 15. As a result, even if the power rollers 8 tend to displace along the axial direction (left-and-right direction in FIG. 23; direction perpendicular to the plane of FIG. 24) of the input shaft 15 due to elastic deformation of the constructural parts based on great loads acting on the constructural parts in accordance with the rotational force transmitting conditions, the displacement can be absorbed without excessive forces on the constructural parts.
Between outer surfaces of the power rollers 8 and inner surfaces of the intermediate portions of the trunnions 6, in order from the outer surfaces of the power rollers 8, there are provided thrust ball bearings (first thrust bearings) 29 and thrust needle bearings (second thrust bearings) 30 which are serially disposed with respect to a thrust force acting direction (up-and-down direction in FIGS. 23 and 24). The thrust ball bearings 29 support the thrust loads acting on the power rollers 8 while permitting rotations of the power rollers 8. Each such thrust ball bearings 29 includes a plurality of balls 31, an annular retainer 32 for rollingly holding the balls 31, and an annular outer race 33. Inner race tracks of the thrust ball bearings 29 are formed in the outer surface of the power rollers 8 and outer race tracks are formed in inner surfaces of the outer races 33.
Each of the thrust needle bearings 30 includes a race 34, a retainer 35, and a plurality of needles 36. The race 34 and the retainer 35 are assembled for slight displacement movement in a rotational direction. Such thrust needle bearings 30 are interposed between inner surfaces of the trunnions 6 and outer surfaces of the outer races 33 in a condition that the races 34 abut against the inner surfaces of the trunnions. Such thrust needle bearings 30 support the thrust loads acting on the outer races 33 while permitting rocking movements of the outer races 33 around the support shaft portions 25.
Further, drive rods 37 are coupled to one ends (left ends in FIG. 24) of the trunnions 6, and drive pistons 38 are secured to outer peripheral surfaces of intermediate portions of the drive roads 37. The drive pistons 38 are mounted within corresponding drive cylinders 39 in an oil-tight manner.
In case of the toroidal type continuously variable transmission having the above-mentioned construction, the rotation of the input shaft 15 is transmitted to the input disc 2 through the urging device 9. The rotation of the input disc 2 is transmitted to the output disc 4 through the pair of power rollers 8, and the rotation of the output disc 4 is taken from the output gear 18. When a rotational speed ratio between the input shaft 15 and the output gear 18 is changed, the pair of pistons 38 are displaced in opposite directions. In response to the displacement of the pistons 38, the pair of trunnions 6 are displaced in opposite directions, with the result that, for example, the lower power roller in FIG. 24 is displaced to the right in FIG. 24 and the upper power roller in FIG. 24 is displaced to the left in FIG. 24. Consequently, directions of tangential forces acting on contact areas between the peripheral surfaces 8a of the power rollers 8 and the inner surfaces 2a, 4a of the input and output discs 2, 4 are changed. In response to the change in the force directions, the trunnions 6 are rocked in opposite directions around pivot shafts 5 supported by the support plates 20. As a result, as shown in FIGS. 21 and 22, the contact positions between the peripheral surfaces 8a of the power rollers 8 and the inner surfaces 2a, 4a are changed, thereby changing the rotational speed ratio between the input shaft 15 and the output gear 18.
When the rotational speed ratio between the input shaft 15 and the output gear 18 is adjusted to a desired value, shift amounts of the pistons 38 are regulated. The regulation of the shift amounts of the pistons 38 is effected by engagement between precess cams (not shown) secured to ends or intermediate portions of the drive rods 37 and spools or sleeves of spool valves (not shown). When the rotational force is transmitted between the input shaft 15 and the output gear 18 as mentioned above, in response to the deformation of the constructural parts, the power rollers 8 are displaced in the axial direction of the input shaft 15, with the result that the displacement shafts 7 pivotally supporting the power rollers 8 are slightly rotated around the support shaft portions 25. As a result of such rotations, the outer surfaces of the outer races 33 of the thrust ball bearings 20 and the inner surfaces of the trunnions 6 are displaced relative to each other. Since the thrust needle bearings 30 are disposed between the outer surfaces and the inner surfaces, a force required for causing the relative rotation is small. Accordingly, as mentioned above, a force for changing the inclined angle of each displacement shaft 7 can be made smaller.
Further, as shown in FIGS. 25 and 26, there has also been proposed constructions in which two input discs 102A, 102B and two output discs 104 are disposed around an input shaft 15 in order to increase torque which can be transmitted and these two input and output discs 102A, 103B, 104 are arranged in parallel with respect to a force transmitting direction. In both constructions shown in FIGS. 25 and 26, an output gear 121a is supported on a periphery of an intermediate portion of an input shaft 115a for rotational movement with respect to the input shaft 115a and the output discs 104 are spline-connected to cylindrical both ends at a center of the output gear 121a. Needle bearings 116 are disposed between inner peripheral surfaces of the output discs 104 and an outer peripheral surface of the input shaft 115a so that the output discs 104 are supported for rotational movement around and with respect to the input shaft 115a and displacement movement in an axial direction of the input shaft 115a. Further, the input discs 102A, 102B are supported on both ends of the input shaft 115a for rotational movement together with the input shaft 115a. The input shaft 115a is rotated by a drive shaft 135 via an urging device 109 of loading cam type. Incidentally, a radial bearing 136 such as a sliding bearing or a needle bearing is disposed between an outer peripheral surface of a distal end (left end in FIGS. 25 and 26) of the drive shaft 135 and an inner peripheral surface of a proximal end (right end in FIGS. 25 and 26) of the input shaft 115a. Accordingly, the drive shaft 135 and the input shaft 115a are assembled so that they can be displaced in the rotational direction in a coaxial relation.
However, a rear surface (left surface in FIGS. 25 and 26) of one 102A (left one in FIGS. 25 and 26) of the input discs abuts against a loading nut 137 directly (in the construction shown in FIG. 26) or via a coned disc spring 151 (in the construction shown in FIG. 25), thereby substantially preventing axial (left-and-right direction in FIGS. 25 and 26) displacement of the input disc with respect to the input shaft 115a. On the other hand, the input disc 102B opposed to a cam plate 110 is supported on the input shaft 115a via a ball spline 138 for axial displacement movement. A coned disc spring 139 and a thrust needle bearing 140 are disposed in series between a rear surface (right surface in FIGS. 25 and 26) of the input disc 102B and a front surface (left surface in FIGS. 25 and 26) of the cam plate 110. The coned disc spring 139 serves to apply pre-pressure to contact areas between inner surfaces 102a, 104a of the discs 102A, 102B, 104 and peripheral surfaces 108a of the power rollers 108. When the urging device 109 is operated, the thrust needle bearing 140 serves to permit relative rotation between the input disc 102B and the cam plate 110.
In case of the construction shown in FIG. 25, the output gear 121a is rotatably supported by a partition wall 141 within a housing via a pair of ball bearings 142 of angular type in a condition that displacement of the output gear is prevented. On the other hand, in case of the construction shown in FIG. 26, the output shaft 121a can freely be displaced in the axial direction. Incidentally, as shown in FIGS. 25 and 26, the reason why the toroidal type continuously variable transmission of so-called double cavity type in which the two input discs 102A, 102B and output discs 104 are disposed in parallel with respect to the power transmitting direction supports one or both of the input discs 102A, 102B via the ball splines 138, 138a for axial displacement movement is that the input discs 102A, 102B can be displaced in the axial direction of the input shaft 115a in response to deformation of the constructural parts caused by the operation of the urging device 9 while rotating the discs 102A, 102B in a synchronous manner.
When the toroidal type continuously variable transmission having the above-mentioned construction is assembled, conventionally, various constructural parts were assembled successively within the housing 40 (FIG. 24) containing the toroidal type continuously variable transmission. Accordingly, positional deviation between the parts due to total dimensional errors of the constructural parts, i.e., the fact whether the constructural parts are operated correctly or not could not be ascertained before all of the constructural parts are completely assembled within the housing 40.
In order to ensure efficiency and endurance of the toroidal type continuously variable transmission, positional relations between the constructural parts must be maintained with high accuracy. Thus, if the positional deviation between the parts due to the total dimensional errors of the constructural parts becomes great, the toroidal type continuously variable transmission once assembled within the housing must be disassembled and re-assembled in order to reduce the positional deviation by combining various parts with other parts.
When the toroidal type continuously variable transmission is assembled in this way, the assembly operation of the toroidal type continuously variable transmission becomes complicated and cost of the transmission cannot be reduced.